The present invention relates to a nondispersive infrared gas analyzer designed for concurrently measuring the concentration of several components within a gas sample and more particularly the invention relates to a nondispersive infrared gas analyzer which is basically comprised of an arrangement that includes a source of infrared radiation, a modulator, a sample and a reference chamber, a pneumatically operating radiation detector which includes two chambers arranged upstream and downstream with respect to each other, each chamber being traversed by radiation that has already passed the sample and the reference chambers.
Gas analysis requires the ascertainment of relatively small measuring components, and often not just one but two or more which fortunately do have not completely coincidental measuring range characteristics (absorption bands). By way of example the measurement of exhaust fumes of automobiles requires a separate determination of carbon monoxide and carbon dioxide whereby by example the fumes may contain 1% by volume of carbon monoxide and about 16% of CO.sub.2. Measuring these different concentrations is made difficult by the fact that the absorption utilized as the measuring effect is basically delineated by a nonlinear function. Consequently the physical length of the sample chamber is a particular parameter that has to be considered; in fact, and in order to provide for adequate sensitivity, the length of these chambers has to be matched to the measuring task to place the range of interest in a portion of the nonlinear characteristics that is not too much curved. A residual linearization can then be provided electrically in the output circuit of the detector and in a manner known per se, using nonlinearly operating and operated electronics component and auxiliary devices.
It follows from the foregoing that the measuring equipment has to be adapted physically to the measuring task which means that for different tasks different gas components one needs different constructions in the gas analyzer or one has to measure the components individually, and still use as many, differently constructed devices and gas analyzers as there are different components to be ascertained. Obviously this is an extensive way to proceed and owing to the multiplicity of functions failure rates or lack of availability of one or the other type is a nonnegligible possibility (see here e.g. German Patent 3,243,301).